The present invention relates to ornamental gemstones and, in particular, it concerns a gemstone having an irregular octagonal girdle and corresponding methods of cutting gemstones.
Many different shapes or “cuts” are known for diamonds and other ornamental gemstones. For the purpose of the present invention, it is convenient to subdivide the known cuts into classes based upon the outline of the girdle as viewed in plan view. Thus, examples of the common gemstone cuts include those having girdles with the following shapes:                round—such as the “Round Brilliant” cut;        regular octagon;        square, such as the “Princess” cut; and        cut-corner rectangle, such as the “Emerald” or “Radiant” cuts.        
One of the many features contributing to the value of a cut gemstone is its weight. A critical factor in the profitability of gemstone cutting is thus the yield, i.e., the percentage of weight from a starting block of gemstone material which remains in the final cut gemstone. In many cases, the starting block from which gemstones are cut is supplied in the form of a square-based pyramid. When cutting a gemstone with a square-symmetry cut, the size of the starting block is clearly chosen to have a base of dimensions corresponding to the desired square cut dimensions. Where a cut with rectangular symmetry is to be used, the starting block is typically chosen to have a square or rectangular base with at least one side of the base of length equal to the desired length of the cut gemstone.
A further feature contributing to the value of a gemstone is its apparent size. In the case of a square-symmetry cut stone, the perceived size is generally gauged by the length of the side of the square outline. In the case of a stone cut with rectangular symmetry, the perceived size is generally gauged by the rectangular outline of “length” times “breadth”.
By way of example, U.S. Pat. No. 5,657,646 to Rosenberg discloses various gemstone cuts with irregular octagonal girdles exhibiting major and minor dimensions. In each case, the minimum size of a starting block from which the gem is cut is clearly a pyramid with a rectangular base having one pair of sides of length equal to the major dimension of the finished gemstone. The perceived size of the gemstone would also be a function of these two dimensions.
There is therefore a need for a gemstone cut and corresponding method for cutting a gemstone which would facilitate relatively high yield and would provide a gemstone with a major dimension greater than the side of a square-based pyramidal block from which it is cut.